It has previously been shown that certain flavin-containing oxidases, in the presence of iron sulfur proteins such as ferredoxin and putaredoxin, are able to oxidatively damage proteins (Stadtman & Wittenberger, 1985). If this type of interaction were a general property of oxidase and iron sulfur protein-containing systems, then this would be a hitherto unidentified mechanism of oxidative damage to the cell. Work in this project, therefore, initially focussed on extending the list of oxidases capable of mediating such damage to include alcohol oxidase, cholesterol oxidase (both flavin and non-flavin forms), and both d- and l-amino acid oxidases. However, when cytoplasmic iron sulfur containing enzymes, including xanthine oxidase and aconitase, which may be expected to come into contact with various oxidases in a physiological setting, were examined for their ability to substitute for ferredoxin in this system, no such damage was evident. It is, therefore, concluded that interaction between iron sulfur proteins and oxidases is unlikely to be a general mechanism of protein damage.